sounds like a good plan.You can fit a rectangle tank approx 300 x 250 x 850 between chassis rails and close to the floor in place of rear muffler. It bolts up with same holes used for the tow bar and still has more clearance than original muffler offered. Tow bar is still used but with longer bolts. Mine is under construction and made out off 2mm stainless sheet. You could also use the tank for fuel instead if desired. Plus the GV sounds much better now with sports muffler in front of rear diff.
You could devise some sort of flexible water bladder and fill up the rear door. Drill and tap a faucet. I wonder how many gallons/liters will fit?I have a 2011 GV that I do a lot of camping in. I'm trying to free up some space in the back by taking out the water containers and putting something under the back of the car, without reducing clearance.
Does anyone have any ideas?